Setting up a WRITE_VAR to bridge through a Ethernet to Modbus gateway in a Unity Premium application.

Goals and Symptoms

Premium, WRITE_VAR

Causes and Fixes

First open your Unity Premium programs Ethernet network configuration



Set the IP configuration as needed for your Ethernet network. Next click the messaging tab.



Set the Network and Station first. Then put the XWAY address you want to use and enter the IP address of the Ethernet to Modbus Bridge/Gateway you will be using.
For more detailed information on messaging please see the Unity Pro help files.
Validate your changes and then open your Ethernet interface for the configuration.



Choose the proper Function and Net Link.
Also make note of the module slot and channel numbers.
Once again validate your changes.



Open your project settings from the tools menu.
Under Language extensions make sure all data types are checked.
This will allow for direct array addressing in the program.


Next place the WRITE_VAR into you program section and fill out the parameters where:

ADR is the addressing pin which directs the WRITE_VAR to the end device.
OBJ is the object type you are trying to read.
NUM is the register address in the slave where the read begins.
NB is the total number of registers to be read.
EMIS is the register location within the Premium where the data to be written is stored.
GEST is the 4 INT array used for the Management Parameters.



The ADR input ADDR('{1.100}0.2.0.1') calls the ADDR block which requires a string input to address the WRITE_VAR correctly.
In this case the string input is '{1.100}0.2.0.1'. Which calls the XWAY address 1.100 (address of the bridge) and Ethernet interface 0.2.0 (rack, slot, channel).
The final 1 is the modbus address of the slave device on the other side of the bridge.